Process for making metallic wires and metallic wires prepared thereby

ABSTRACT

Small watch springs are manufactured from wire rod by means of a cold-drawing operation whereby the final cross-sectional, strip dimension is obtained without cold-rolling. The cold-drawing operation aligns and maintains the alignment of the crystallographic axes lengthwise along the strip and thereby optimizes the spring properties of the cold-drawn strip.

limited States Patent Ange [ 1 Feb.29,1972

[S4] PROCESS FOR MAKING METALLIC WIRES AND METALLIC WIRES PREPARED THEREBY [56] References Cited UNITED STATES PATENTS 3,394,036 7/1968 Parris ..72/ 364 2,859,149 11/1958 Straumann. 72/700 9/1939 Wasson 1/1910 Bolton ..29/173 Primary Examiner-Charles W. Lanham Assistant Examiner-Michael J. Keenan I Attorney-Robert E, Burns and Emmanuel J. Lobato [57] I ABSTRACT Small watch springs are manufactured from wire rod by means of a cold-drawing operation whereby the final cross-sectional, strip dimension is obtained without cold-rolling. The colddrawing operation aligns and maintains the alignment of the crystallographic axes lengthwise along the strip and thereby optimizes the spring properties of the cold-drawn strip.

12 Claims, 4 Drawing Figures PROCESS FOR MAKTNG METALLIC WIRES AND METALLIC WIRES PREPARED THEREBY This application is a continuation-in-part of my copending application, Ser. No. 615,424, filed Feb. 13, 1967, now abandoned.

The present invention relates to a process for the manufacture of watch springs, especially for small watches, and more particularly to a method of making watch springs whereby the final cross-sectional configuration of the spring is obtained by cold drawing.

Conventional wristwatch springs usually have a width of from 1 to 2 mm. and a thickness of about 0.05 to 0.15 mm. and are typically cut to the required length from metal strips which were previously rolled to the proper width. This method presents various disadvantages, one significant one being that the proper strips rolled to the proper width exhibit fluctuations in gauge and hence, springs cut out from such strips have an undesirable thickness tolerance. Moreover, sharp edges occur during the cutting, requiring a special subsequent process for rounding them off. In addition, the rolling operation does not optimize the spring properties ofthe metal strip and therefore is not the most suitable process for preparing springs.

These disadvantages are partially avoided by another wellknown method of spring manufacture, as described in U.S. Pat. No. 2,859,149. This manufacturing process, which is derived from the manufacture of larger-dimensioned springs, consists in flat-rolling a previously cold-drawn wire rod to the required dimensions. Generally, spring steel of a better quality than that used for larger springs is employed, such as a ferrocarbon alloy treated by the so-called patenting process, known also as textural steel, or stainless alloys.

According to the cold-drawing followed by cold-rolling fabrication of small springs discussed in US. Pat. No. 2,859,149, a certain optimum range of spring properties is obtainable provided the ratio of the reduction in cross section through cold drawing of the rod to the cross-sectional shrinkage in the subsequent cold rolling is kept within well-defined limits and provided the total decrease in cross-sectional area exceeds 80 percent. Likewise, a precise ratio must be maintained between the tensile strength of the predrawn rod and the rod diameter. The pronounced decrease in cross-sectional area produces a fairly high ultimate strength, which is further enhanced by a subsequent heat treatment. Unfortunately, the properties of the springs thus obtained will be markedly worse if the aforementioned conditions, which are frequently extremely difficult to comply with, are not strictly observed.

One disadvantage of the known processes wherein the final dimension of the spring is obtained by cold rolling is that during reduction of the cross-sectional area by cold drawing, a considerable and desirable straightening of the crystallographic axis structure takes place in the direction of elongation, but such desirable alignment of the crystallographic axis is thereafter upset by the subsequent flat rolling. A considerable widening of the spring occurs during flat rolling to the final spring cross section, and such fiat rolling necessarily results in a deflection of the crystallographic axis away from the direction of rolling. Thus, for example, as stated in U.S. Pat. No. 2,859,149, a typical cold-worked wire of 0.6-mm. thickness widens to 1.5 mm. in the subsequent cold-rolling process, representing a spread of 250 percent. Obviously, with such expansion, no significant satisfactory alignment of the crystallographic axis in the longitudinal direction of the strip is possible for procuring optimum spring properties and the desirable crystal alignment attained through the preceding cold working is subsequently severely disturbed.

Moreover, during the cold rolling of thin wires to their final dimensions, a roughness developes along their edges and the edges also tend to tear or spread. Furthermore, the finished cold-rolled strips come out with a more or less convex shape. For these reasons, many spring manufacturers find it necessary to subsequently grind down the lateral edges of the strips, which are thinner than the central region, necessitating the rolling'of the strips to a somewhat wider dimension than the actual, final width of the spring.

It is a primary object of the present invention to avoid the above-mentioned disadvantages connected with the known manufacturing methods for producing small watch springs by providing a process for achieving optimum lengthwise orientation of the crystallographic axes in the spring strip.

It is a further object of the present invention to completely eliminate the need for cold-rolling a spring strip in its high stress range.

The present invention comprises selecting a wire rod which is suitable for use as a small watch spring and forming the final cross-sectional area of the spring by cold drawing. The ultimate set of the original wire rod thus results from flat drawing, and this should be distinguished from flat rolling. The drawing procedure is preferably completed in several steps, for example, from eight to 12 individual steps. Between the individual cold-drawing steps, intermediate annealing steps at temperatures of from 200 to 280 C. may advantageously be carried out, depending upon the material employed, though this is not in any way a necessary step. Dependent upon the spring stock used, the wire rod to be processed is first subjected to a suitable, known thermal pretreatment and after the flat drawing, the spring strip is subjected to a known thermal aftertreatment Both thermal treatments are well known in the art.

If the desired width of the final spring strip is substantially greater than the initial diameter of the particular wire rod to be used, it is desirable to first decrease the cross-sectional area of the wire rod by 40 to 70 percent, preferably by cylindrical drawing to ensure that it remains free from any high stress and then, prior to the final flat drawing, to moderately cold roll the strip to obtain the approximate rectangular cross section which is desired. It should be emphasized that this intermediate cold rolling takes place in a low range of stress, for example, at wire tenacities lower than 170 kg./mm. so that all the disadvantages involved in cold rolling at a high range of stress, especially convex camber of the strip, are thoroughly avoided. The final strip dimensions are subsequently obtained by flat drawing which simultaneously imparts to the strip the required optimum orientation of the crystallographic axes in the direction of pull to thereby maximize the spring properties of the metal strip.

FIGS. 1-4 show various cross-sectional shapes for finished springs according to the present invention;

FIG. 1 is a cross-sectional view of a metal strip having a rectangular configuration;

FIG. 2 is a cross-sectional view similar to FIG. 1 but showing a rectangular strip with rounded corners;

FIG. 3 is a cross-sectional view similar to FIG. 2 but showing a concavely shaped metal strip; and

FIG. 4 is a cross-sectional view of a metal strip having an elliptical configuration.

The process according to the invention is explained hereinafter in greater detail in conjunction with the following five examples from which other objects and advantages of the present invention will become apparent:

EXAMPLE 1 A spring strip 1.15X0. l 35 mm. in final cross section was manufactured from a textural steel (patented wire") rod having 0.85 percent carbon content, an initial diameter of approximately 1.5 mm., and a tenacity of less than 160 kgJmm. by the following steps:

a. Circular drawing until the cross-sectional area of the wire decreased to about 65 percent of its original diameter (about 0.95 mm.), corresponding to a wire tenacity of 179 kg./mm.

b. Flat-drawing the wire until its cross-sectional area decreased another 26.3 percent (91.3 percent altogether) and the desired cross-sectional dimension of 1.15 mm.X0. mm. was achieved, which correspondingly increased the tenacity to 270 kgJmmF; and

c. Heat-treating the wire strip for about 1 hour at approximately 250 C., thus increasing the tenacity to 281 kg./mm.

The width of the finished spring strip amounted therefore to about one-half and the thickness to about 0.14 of the initial diameter of the wire before flat drawing.

Torsions measured on this spring strip amounted to minus 0.1 turns or minus four turns of the completely coiled spiral spring in the sense of a slackening (corresponding therefore to 0.1 or four turns of the spring barrel of the tightened spring in the sense of a slackening of spring), 1,020 or 847 mm. total.

in comparison, a spring strip having the same final crosssectional dimension was produced from the same material by cold-rolling, as follows:

A wire rod of approximately 1.5-mm. diameter was first cylindrically drawn until its cross-sectional area decreased 88 percent, corresponding to a diameter of about 0.51 mm. and a tenacity of 204 kg./mm. Then the wire strip was further decreased in cross-sectional area (about another 3.5 percent) by flat rolling to its final dimension of 1.l5 0.135 mm. The width of this spring strip amounted to about 2.25 and its thickness to about 0.25 times the initial wire diameter prior to flat rolling. After the same subsequent heat treatment, the spring strip had a tenacity likewise of approximately 280 kg./mm. as above, however, the torsions amounted to minus 0.1 or minus four turns, only 997 or 834 mm. total of the spring spiral, while the number of winding cycles (periodic winding and slackening of the spring) until the spring fractured was about 20 percent less than in the case of the spring treated in accordance with the invention.

EXAMPLE 2 A spring strip having a final cross section 1.5X0.0725 mm. was manufactured from the same textural steel as used in Example I, though of somewhat less diameter, by the following steps:

a. Cylindrical drawing until the cross-sectional area decreased 47 percent corresponding to a wire diameter of about 0.95 mm., and a tenacity of 160 kg./mm.

b. Intermediate flat-rolling of the wire to further decrease the cross-sectional area another 3.6 percent and correspondingly the tenacity to 184 kg./mm.

e. Flat-drawing the wire to further decrease the cross-sectional area by 40.6 percent and to thereby attain the final dimensions, corresponding to a tenacity of255 kg./mm.

d. Heat-treating the drawn wire strip at approximately 250 C. for an hour to increase the tenacity to 272 kg./mm.

The width of the finished spring strip is therefore equivalent to approximately 1.6 times the initial diameter of the wire before flat rolling or approximately 1.08 times the width of the rough strip, and the thickness of the finished spring strip is approximately 0.076 times the initial diameter of the wire before flat rolling or 0.18 times the thickness of the rough strip.

Torsions measured at minus 0.1 or minus four turns of the wound spiral spring amounted to 313 to 260 mm. total. The number of winding cycles until fracture of the spring was (from several similar experiments) 4,906.

In comparison, a spring strip having the same final crosssectional dimension was produced by rolling from the same material, as follows:

A wire rod was first cylindrically drawn to decrease the cross-sectional area by 90.8 percent to a diameter of about 0.42 mm. and a tenacity of 225 kg./mm. and then the crosssectional area was further decreased another 3.7 percent by flat-rolling the wire rod to its final size. The width of this spring strip is thus approximately 3.6 times and its thickness about 0.17 times the initial diameter of the wire prior to flat rolling. After the subsequent heat treatment the tenacity amounted to 270 kg./mm.

The comparative torsions of this spring were in the region of only 300 to 237 mm. total, while fracture of the spring occurred at 3,354 winding periods. That is to say, the endurance of the spring manufactured in accordance with the present invention is approximately 46 percent greater than that of springs manufactured in the conventional way.

EXAMPLE 3 A patent 0.88 percent carbon content wire was cold-drawn to a diameter of 1.5 mm. and a tenacity of 161 kg./mm. in 11 steps until the cross-sectional area was decreased percent and a strip width of 1.52 mm. was obtained. The tenacity of the finished spring strip after a subsequent heat treatment amounted to 256 kg./mm.

In a comparative test from a piece of the same wire, a total decrease in cross-sectional area of only 55 percent could be reached by cold-rolling, since at that point, burring of the edges was noted. The rolled wire as at this point widened to 2.50 mm. and its tenacity amounted to only 210 kg./mm.

EXAMPLE 4 A wire made of the alloy having the trade name PHYNOX (Co 40, Cr 20, Ni 16, Fe 15.57, M0 6.5, Mn 1.5, Si 0.3 and C 0.13), was first annealed in the usual manner at 800850 C. and then cooled off to room temperature, and thus had an initial diameter of 1.5 mm. and an initial tenacity of 101.5 kg./mm. The wire was then cold-drawn until its cross-sectional area was decreased by 67 percent and its width was changed to about 1.52 mm. After the customary heat treatment for this alloy, at about 520 C. for an hour, a tenacity of 260 kg./mm. was measured.

The cross section ofa similar piece of wire could be reduced only 48 percent by rolling, and the tenacity measured after the customary heat treatment amounted to 255 kg./mm.

EXAMPLE 5 A PHYNOX wire, similar to the sample used in Example 4, having an initial diameter of 1.2 mm. and an initial tenacity of 124 kg./mm. was decreased in cross section to 71 percent of its original area by cold-drawing and the resulting tenacity after heat treatment was 275 kg./mm. in comparison, a piece of the same wire after cold-rolling was reduced in cross-sectional area by 51 percent and the corresponding tenacity after heat treatment amounted to only 234 kg./mm.

In Examples 3-5, the useful life and torsions of the spring samples made according to the process of the present invention were higher than the corresponding spring samples produced by the conventional cold-rolling process.

The above-cited examples show that watch springs manufactured according to the process of the present invention exhibit substantially better spring properties in comparison with watch springs made by the conventional methods. Especially noteworthy is the fact that the width of spring strip obtained by cold-drawing is at most only 20 percent to 25 percent, greater than the diameter of the wire before flat-drawing, and frequently only 5 percent greater. Hence, the considerable decrease in the cross-sectional area of the spring strip by-cold drawing is produced by an end-to-end stretching of the strip and not by a deliberate widening operation and it is therefore evident that the spring strip made according to the present invention has an excellent orientation of the crystallographic axes along the longitudinal axis of the strip which results in superior spring properties. Radiographic tests have shown that the crystal structure of the cold-drawn spring strip is better than that obtainable by cold-rolling, even when cold-rolled under optimal conditions in accordance with the process described in the U.S. Pat. No. 2,859,149.

The cold-drawing process of the present invention can be carried out in several steps by using suitably chosen and wellknown drawing orifices. The particular drawing speed depends upon the type of material constituting the spring strip and preferably is carried out at speeds between 15 m. to 20 in. per minute and may reach a speed of 40 meters per minute provided the temperature in the orifices does not exceed about 200 C. Temperatures in excess of 200 C. detrimentally affect the spring strip.

Between the individual steps as well as after the intermediate flat-rolling steps, an intermediate annealing treatment may be employed depending upon the properties of the particular spring material being used.

The process of the present invention is applicable to all known spring materials, among which belong the family of stainless and nonmagnetic alloys, including nickel-chrome steels and cobalt-chrome alloys, such as the PHYNOX alloy mentioned above, and the group of oxidizable and magnetic stock which includes the aforesaid textural steels and finished refined steels having approximately l8 percent Ni and 9 percent Co. A typical example for a finished refined alloy heattreated, for instance, for 3 hours in a temperature range of 450 C. to 480 C., is the alloy known under the trade name DURIMPHY with 32.18 Fe, 18.00 Ni, 8.70 Co, 4.75 No, 0.20 Al, 0.07 Mn, 0.030 Si and 0.030 C.

it has generally proved practical that the tenacity of the wire to be processed according to this invention, with diameters between approximately 0.8 and 2.0 mm., should amount to 150 to 190 kg./mm. before flattening in the case of textural steel, and 100 to 150 kgJmm. in the case of nonoxidizing alloys, in which the higher initial tenacities should be used with the smaller-diameter wire, and vice versa. If the stock at disposal, which is to be processed by flat-drawing, does not yet have the stated tenacity values, then, as described in Examples l and 2, the tenacity is first increased by cylindrical drawing accompanied by a corresponding decrease in cross-sectional area. A possible flat-rolling before the final flat-drawing ought to be given only with wire tenacitys under 170 kg./mm.

The suitable thermal pretreatment of the wire in any given case and the thermal final treatment of heat-treated spring strip, and if need be, the intermediate annealing between the drawing stages or after intermediate flat-rolling, depend on the selected wire stock and pertain to the known state of the art. On this point, for instance, refer to the steel wire textbook Stahldraht" by Anton POMP, published by Stahleisen" G.m.b.l-l.(lnc.), Dusseldorf, 1962.

What] claim and desire to secure by Letters Patent is:

1. A process for manufacturing spring strip to be converted into watch springs from wire rod comprising: providing a Wire rod of cylindrical cross section preheat-treated to render it effective for use as watch spring material; cold flat drawing said wire rod to its final generally rectangular cross-sectional strip dimensions to align and maintain the alignment of its crystallographic axes in the longitudinal direction of the strip; and

heat-treating the cold-drawn strip to further improve its effectiveness as a watch spring.

2. A process according to claim 1; wherein said wire rod is textural steel having a diameter between 0.8 and 2.0 mm. and a tenacity within the range of 150 to 190 kg./mm.

3. A process according to claim I; wherein said wire rod is textural steel having a diameter greater than 2.0 mm. and a tenacity less than 150 kgjmm. and further including the step of cylindrically drawing said wire rod to a diameter of between 0.8 and 2.0 mm. and a tenacity within the range of 150 to 190 kg./mm. prior to said cold-drawing.

4. A process according to claim 3; wherein said cylindrical drawing decreases the cross-sectional area of said wire rod by 40 to 70 percent.

5. A process according to claim 1; wherein said wire rod is a nonoxidizable alloy having a diameter between 0.8 and 2.0 mm. and a tenacity within the range of to kg./mm.

6. A process according to claim 1; wherein said wire rod is a nonoxidizable alloy having a diameter greater than 2.0 mm. and a tenacity less than 100 kg./mm. and further including the step of cylindrically drawing said wire rod to a diameter of between 0.8 and 2.0 mm. and a tenacity within the range of 100 to I50 kg./mm. prior to said cold-drawing.

7. A process according to claim 6; wherein said cylindrical drawing decreases the cross-sectional area of said wire rod by 40 to 70 percent.

8. A process according to claim I; further including both cylindrically drawing said wire rod to decrease its cross-sectional area by 30 to 60 percent and flat-rolling the cylindrically drawn wire rod to further decrease its cross-sectional area by 2 to 8 percent prior to said cold drawing; and wherein said cold drawing still further decreases the cross-sectional area by 30 to 60 percent.

9. A process according to claim 1; wherein said cold drawing decreases the cross-sectional area of said wire rod by 60 to 90 percent.

10. A process according to claim 1; wherein said cold drawing increases the width of said wire rod by an amount not greater than 25 percent of its precold drawn width.

11. A process according to claim 1; wherein said cold drawing is performed in several steps.

12. A process according to claim 11; further including heat treating the cold-drawnrod after each cold-drawing steps. 

1. A process for manufacturing spring strip to be converted into watch springs from wire rod comprising: providing a Wire rod of cylindrical cross section preheat-treated to render it effective for use as watch spring material; cold flat drawing said wire rod to its final generally rectangular cross-sectional strip dimensions to align and maintain the alignment of its crystallographic axes in the longitudinal direction of the strip; and heat-treating the cold-drawn strip to further improve its effectiveness as a watch spring.
 2. A process according to claim 1; wherein said wire rod is textural steel having a diameter between 0.8 and 2.0 mm. and a tenacity within the range of 150 to 190 kg./mm.2.
 3. A process according to claim 1; wherein said wire rod is textural steel having a diameter greater than 2.0 mm. and a tenacity less than 150 kg./mm.2 and further including the step of cylindrically drawing said wire rod to a diameter of between 0.8 and 2.0 mm. and a tenacity within the range of 150 to 190 kg./mm.2 prior to said cold-drawing.
 4. A process according to claim 3; wherein said cylindrical drawing decreases the cross-sectional area of said wire rod by 40 to 70 percent.
 5. A process according to claim 1; wherein said wire rod is a nonoxidizable alloy having a diameter between 0.8 and 2.0 mm. and a tenacity within the range of 100 to 150 kg./mm.2.
 6. A process according to claim 1; wherein said wire rod is a nonoxidizable alloy having a diameter greater than 2.0 mm. and a tenacity less than 100 kg./mm.2 and further including the step of cylindrically drawing said wire rod to a diameter of between 0.8 and 2.0 mm. and a tenacity within the range of 100 to 150 kg./mm.2 prior to said cold-drawing.
 7. A process according to claim 6; wherein said cylindrical drawing decreases the cross-sectional area of said wire rod by 40 to 70 percent.
 8. A process according to claim 1; further including both cylindrically drawing said wire rod to decrease its cross-sectional area by 30 to 60 percent and flat-rolling the cylindrically drawn wire rod to further decrease its cross-sectional area by 2 to 8 percent prior to said cold drawing; and wherein said cold drawing still further decreases the cross-sectional area by 30 to 60 percent.
 9. A process according to claim 1; wherein said cold drawing decreases the cross-sectional area of said wire rod by 60 to 90 percent.
 10. A process according to claim 1; wherein said cold drawing increases the width of said wire rod by an amount not greater than 25 percent of its precold drawn width.
 11. A process according to claim 1; wherein said cold drawing is performed in several steps.
 12. A process according to claim 11; further including heat treating the cold-drawn rod after each cold-drawing steps. 